This file describes the changes from Expect 3 to Expect 4.
The improvements that people will find most interesting are:
1) Expect version 4 is designed to work with Tcl 6.7 and Tk 3.2.
(Earlier versions of Expect will not work with Tcl 6.7)
Expect can now be layered in with any Tcl program.
Note that in Tk, Expect's send command is called "exp_send".
(It used to be called "send_spawn" but this bit the dust.)
2) A debugger is provided.
3) The interact command has been totally rewritten and supports regular
expressions, timeout/eof patterns, and a number of other new things.
4) The default behavior of ^C (SIGINT) is exit whether or not you are in
a read.
5) Expect uses "sane" terminal parameters by default, allowing scripts
to work the same whether inside emacs shell mode or not. (See man
page on "spawn" for more info.)
6) All the hard parts of the installation process are automated. This
was done primarily by Rob Savoye at Cygnus. Thank you, Rob!
7) It is now possible to buy a support contract for Expect from Cygnus.
The changes that people will find most annoying are:
1) send now only sends a single string. (It used to send any number of
strings with spaces jammed in between.)
2) getpid was renamed pid.
3) interact's -flush was renamed -nobuffer (much more descriptive).
4) interact now runs all actions in raw mode unless the flag -reset
is used. -f and -F are ignored. send automatically understands
how to do the right thing. The most likely thing to watch out for
are actions like "exec kill -STOP 0" which almost certainly need
the -reset flag.
5) argv0 is initialized to script name. argv no longer contains it.
argc is initialized [llength $argv]. This follows new Tcl style.
All differences are described in the man page. Some of the less
significant differences are described in the HISTORY file. The
debugger is described in a separate document (see the README).
This version also introduces one incompatibility that may require
changes to scripts. While this may initially annoy you, the final
result will simplify the process of writing scripts. Namely:
In version 3, the expect command accepted lists of glob-style patterns
such as:
expect "a\ b c" action
where "a b" or "c" would cause action to be executed. The problem
with this is that the pattern list is hard to write and hard to read.
Patterns with control-characters, backslashes and dollar signs were
very difficult to deal with.
Regular-expression patterns provide a much simpler solution. Via the
alternation feature (using a "|") the above pattern can be written as:
expect -re "a b|c" action
I was concerned about people having a significant investment in code
that depended on the old syntax but responders to a comp.lang.tcl poll
about such a change in pattern handling were 100% in favor of it. (I
even proposed hooks for backward compatibility, but there was no
interest in it.)
Fortunately, most simple things will work as before including:
expect foobar
expect {foobar}
expect "foobar"
expect "foo\ bar"
However, some things won't work as before. For example, the following
will behave differently - now the braces will be considered as part of
the pattern.
expect "{foo bar}"
Here are examples of patterns in my own code that I had to change:
was changed to
Version 3 pattern list Version 4 pattern
{Whois:\ } "Whois: "
{No\ match} "No match"
{250*ftp>* 200*ftp>*} -re "2(5|0)0.*ftp>.*"
{{Press Return to continue*}} "Press Return to continue*"
{*\r\n*\\\\\r\n} "\r\n*\\\r\n"
Future Change Alert
John Ousterhout has pre-announced a future change in Tcl that may
affect you. In particular, backslash sequences other than those
explicitly listed in the Tcl documentation will be handled as if the
backslash was not present.
The likely place this arises is when quoting characters that are
special to the pattern matcher but not to Tcl.
For example in Tcl 6.7, the following command matches a period.
expect -re "\."
In Tcl 7.0, it will match any character, because Tcl will throw away
the backslash. If you want to match a period, you will have to say:
expect -re "\\."
or
expect -re {\.}
The following command will find occurrences of this. (It may find
other things, but it will at least find the problem cases.)
egrep '(\\$)|(\\[^][bfnrtv\0-9{}$ ;"])' *.exp